Germanosilicate SSZ-75

ABSTRACT

The present invention relates to new germanosilicate SSZ-75 molecular sieve, and methods for synthesizing germanosilicate SSZ-75.

TECHNICAL FIELD

The present invention relates to new germanosilicate molecular sieveSSZ-75 and methods for synthesizing the same.

BACKGROUND

Molecular sieves having the STI framework topology defined by theconnectivity of the tetrahedral atoms (referred to herein simply as“STI”) are known. See, for example, Ch. Baerlocher et al., Atlas ofZeolite Framework Types, 6th Revised Edition, 2007 of the InternationalZeolite Association. Examples of STI molecular sieves include naturallyoccurring stilbite, the zeolite designated TNU-10, and the molecularsieve designated SSZ-75. Stilbite is disclosed by D. W. Breck, ZeoliteMolecular Sieves: Structure Chemistry and Use 1984, Robert E. KriegerPublishing Company. TNU-10 is reported by S. B. Hong et al., J. Am.Chem. Soc. 2004, 126, 5817-5826. SSZ-75 is disclosed in U.S. Pat. No.7,713,512.

Because of their unique sieving characteristics, as well as theircatalytic properties, crystalline molecular sieves and zeolites areespecially useful in applications such as hydrocarbon conversion, gasdrying and separation. Although many different crystalline molecularsieves have been disclosed, there is a continuing need for new molecularsieves with desirable properties for gas separation and drying,hydrocarbon and chemical conversions, and other applications. Newmolecular sieves may contain novel internal pore architectures,providing enhanced selectivity in these processes.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided acrystalline molecular sieve having STI topology and having silicon togermanium mole ratio of less than 15.

The present invention further provides such a crystalline molecularsieve having a composition comprising, as-synthesized and in itsanhydrous state, in terms of mole ratios, the following:

Si/Ge <15 M_(2/n)/Si   0 to 0.03 Q/Si 0.02 to 0.08 F/Si 0.01 to 0.04wherein M is an alkali metal cation, an alkaline earth metal cation or amixture thereof; n is the valence of M; Q is atetramethylene-1,4-bis-(N-methylpyrrolidinium) dication; and F isfluoride.

The present invention also includes a method of preparing a molecularsieve, the method comprising contacting under crystallization conditionsa source of silicon; a source of germanium; a source of fluoride ions;and a structure directing agent comprising atetramethylene-1,4-bis-(N-methylpyrrolidinium) dication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the powder X-ray diffraction (XRD) pattern of theas-synthesized germanosilicate SSZ-75 product of Example 1.

FIG. 2 shows the scanning electron microscopy (SEM) image of theas-synthesized germanosilicate SSZ-75 product of Example 1.

FIG. 3 shows the powder XRD pattern of the as-synthesizedgermanosilicate SSZ-75 product of Example 2.

FIG. 4 shows the SEM image of the as-synthesized germanosilicate SSZ-75product of Example 2.

DETAILED DESCRIPTION

The present invention comprises a molecular sieve designated herein“molecular sieve SSZ-75” or simply “SSZ-75.”

In preparing the germanosilicate SSZ-75 of the invention, atetramethylene-1,4-bis-(N-methylpyrrolidinium) dication is used as astructure directing agent (“SDA”), also known as a crystallizationtemplate. The SDA useful for making germanosilicate SSZ-75 has thefollowing structure:

The SDA dication is associated with anions (X) which may be any anionthat is not detrimental to the formation of the molecular sieve.Representative anions include halogen (e.g., fluoride, chloride, bromideand iodide), hydroxide, acetate, sulfate, tetrafluoroborate,carboxylate, and the like. Typically, the anion is hydroxide. The SDAmay be used to provide hydroxide ion. Thus, it is beneficial to ionexchange, for example, a halide to hydroxide ion.

The tetramethylene-1,4-bis-(N-methylpyrrolidinium) dication SDA can beprepared by a method similar to that described in U.S. Pat. No.5,166,111, which discloses a method for preparing abis(1,4-diazoniabicyclo[2.2.2]octane) alpha omega alkane di-quaternaryammonium ion component, or U.S. Pat. No. 5,268,161, which discloses amethod for preparing 1,3,3,8,8-pentamethyl-3-azoniabicyclo[3.2.1]octanecation.

In general, germanosilicate SSZ-75 is prepared by contacting a source ofsilicon, and a source of germanium with thetetramethylene-1,4-bis-(N-methylpyrrolidinium) dication SDA in thepresence of fluoride ion.

Typical sources of silicon (Si) include silica hydrogel, silicic acid,colloidal silica, tetraalkyl orthosilicates (e.g., tetraethylorthosilicate), silica hydroxides, and fumed silicas.

Typical sources of germanium (Ge) include germanium oxide, germaniumalkoxides (e.g., germanium ethoxide, germanium isopropoxide), germaniumchloride and sodium germanate.

Typical sources of fluoride (F) include ammonium fluoride, hydrofluoricacid, and other suitable fluoride-containing compounds.

Germanosilicate SSZ-75 is prepared from a reaction mixture comprising,in terms of mole ratios, the following:

Si/Ge  5 to 50 OH/Si 0.20 to 0.80 Q/Si 0.10 to 0.40 M_(2/n)/Si   0 to0.04 H₂O/Si  2 to 10 F/Si 0.20 to 0.80wherein M is an alkali metal cation, an alkaline earth metal cation or amixture thereof; n is the valence of M (i.e., 1 or 2); Q is atetramethylene-1,4-bis-(N-methylpyrrolidinium) dication; and F isfluoride. In one embodiment, the reaction mixture has a Si to Ge moleratio of from 5 to 30. Optionally, the reaction mixture may furthercomprise a source of aluminum.

In practice, germanosilicate SSZ-75 is prepared by a process comprising:preparing an aqueous solution containing a source of silicon, a sourceof germanium, a source of fluoride ions, and atetramethylene-1,4-bis-(N-methylpyrrolidinium) dication having ananionic counter-ion which is not detrimental to the formation of themolecular sieve; maintaining the aqueous solution under conditionssufficient to form crystals of the molecular sieve; and recovering thecrystals of the molecular sieve.

The reaction mixture is maintained at an elevated temperature until thecrystals of the germanosilicate SSZ-75 are formed. The hydrothermalcrystallization is usually conducted under autogenous pressure, at atemperature between 100° C. and 200° C., typically between 150° C. and180° C. The crystallization period is typically greater than 1 day andoften from 3 days to 20 days. The molecular sieve may be prepared usingmild stirring or agitation.

During the hydrothermal crystallization step, the germanosilicate SSZ-75crystals can be allowed to nucleate spontaneously from the reactionmixture. The use of SSZ-75 crystals as seed material can be advantageousin decreasing the time necessary for complete crystallization to occur.In addition, seeding can lead to an increased purity of the productobtained by promoting the nucleation and/or formation of germanosilicateSSZ-75 over any undesired phases. When used as seeds, SSZ-75 crystalsare added in an amount between 0.1 and 5% of the weight of the source ofsilicon used in the reaction mixture.

Once the molecular sieve crystals have formed, the solid product isseparated from the reaction mixture by standard mechanical separationtechniques such as filtration. The crystals are water-washed and thendried, e.g., at 90° C. to 150° C. for from 8 to 24 hours, to obtain theas-synthesized germanosilicate SSZ-75 crystals. The drying step can beperformed at atmospheric pressure or under vacuum.

Germanosilicate SSZ-75 has a composition, as-synthesized (i.e., prior toremoval of the SDA from the molecular sieve) and in its anhydrous state,comprising the following (in terms of mole ratios):

Si/Ge <15 M_(2/n)/Si   0 to 0.03 Q/Si 0.02 to 0.08 F/Si 0.01 to 0.04wherein M is an alkali metal cation, alkaline earth metal cation ormixture thereof; n is the valence of M (i.e., 1 or 2); Q is atetramethylene-1,4-bis-(N-methylpyrrolidinium) dication; and F isfluoride.

Germanosilicate SSZ-75 (whether in the as-synthesized or calcinedversion) has a Si to Ge mole ratio of less than 15, for example, from 2to 13 or from 3 to 12.

Germanosilicate SSZ-75 has the STI framework topology. It ischaracterized by its XRD pattern. Germanosilicate SSZ-75,as-synthesized, has a crystalline structure whose powder XRD patternexhibits the characteristic lines shown in Table 1.

TABLE 1 2-Theta d-Spacing Relative Integrated (degrees)^((a))(Angstroms) Intensity (%)^((b)) 9.92 8.91 VS 19.31 4.59 M 20.95 4.24 M22.22 3.99 VS 24.09 3.69 W 26.37 3.38 M 28.24 3.16 M 29.09 3.07 W 29.992.98 M ^((a))±0.20 ^((b))The X-ray patterns provided are based on arelative intensity scale in which the strongest line in the X-raypattern is assigned a value of 100: W (weak) is less than 20; M (medium)is between 20 and 40; S (strong) is between 40 and 60; VS (very strong)is greater than 60.

Table 1A below shows the powder XRD lines for as-synthesizedgermanosilicate SSZ-75 including actual relative intensities.

TABLE 1A 2-Theta d-Spacing Relative Integrated (degrees)^((a))(Angstroms) Intensity (%) 7.03 12.57 4.1 8.09 10.91 2.3 8.96 9.86 2.69.92 8.91 62.4 13.07 6.77 2.9 14.67 6.03 2.7 17.02 5.20 8.9 19.31 4.5938.0 20.18 4.40 3.4 20.95 4.24 20.1 22.22 4.00 100.0 24.10 3.69 14.125.90 3.44 3.0 26.37 3.38 21.6 28.24 3.16 25.5 29.09 3.07 9.9 29.99 2.9828.7 32.24 2.77 2.2 33.38 2.68 7.3 34.87 2.57 8.4 35.46 2.53 5.3 36.312.47 1.3 38.75 2.32 1.9 40.89 2.21 5.3 ^((a))±0.20

After calcination, the powder XRD pattern for germanosilicate SSZ-75exhibits the characteristic lines shown in Table 2 below.

TABLE 2 2-Theta d-Spacing Relative Integrated (degrees)^((a))(Angstroms) Intensity (%)^((b)) 10.00 8.83 VS 13.14 6.73 W 19.38 4.58 M21.03 4.22 M 22.35 3.97 VS 24.19 3.68 W 26.43 3.36 M 28.37 3.14 W 30.162.96 M ^((a))±0.20 ^((b))The X-ray patterns provided are based on arelative intensity scale in which the strongest line in the X-raypattern is assigned a value of 100: W (weak) is less than 20; M (medium)is between 20 and 40; S (strong) is between 40 and 60; VS (very strong)is greater than 60.

The powder XRD patterns were determined by standard techniques. Theradiation was CuKα radiation. The peak heights and the positions, as afunction of 20 where θ is the Bragg angle, were read from the relativeintensities of the peaks, and d, the interplanar spacing in Angstromscorresponding to the recorded lines, can be calculated.

The variation in the scattering angle (2-theta) measurements, due toinstrument error and to differences between individual samples, isestimated at ±0.20 degrees.

Representative peaks from the XRD pattern of as-synthesizedgermanosilicate SSZ-75 are shown in Table 1. Calcination can result inchanges in the intensities of the peaks as compared to patterns of the“as-synthesized” material, as well as minor shifts in the diffractionpattern.

The crystalline germanosilicate SSZ-75 can be used as-synthesized, butpreferably will be thermally treated (calcined). Usually, it isdesirable to remove the alkali metal cation (if any) by ion exchange andreplace it with hydrogen, ammonium, or any desired metal ion. Calcinedgermanosilicate SSZ-75 has an n-hexane adsorption of about 0.16 cc/g.

Germanosilicate SSZ-75 can be formed into a wide variety of physicalshapes. Generally speaking, the molecular sieve can be in the form of apowder, a granule, or a molded product, such as extrudate having aparticle size sufficient to pass through a 2-mesh (Tyler) screen and beretained on a 400-mesh (Tyler) screen. In cases where the catalyst ismolded, such as by extrusion with an organic hinder, the germanosilicateSSZ-75 can be extruded before drying, or, dried or partially dried andthen extruded.

Germanosilicate SSZ-75 can be composited with other materials resistantto the temperatures and other conditions employed in organic conversionprocesses. Such matrix materials include active and inactive materialsand synthetic or naturally occurring zeolites as well as inorganicmaterials such as clays, silica and metal oxides. Examples of suchmaterials and the manner in which they can be used are disclosed in U.S.Pat. Nos. 4,910,006 and 5,316,753.

Germanosilicate SSZ-75 may be useful as an adsorbent for gas separations(owing to its high pore volume while maintaining diffusion control andhydrophobicity). Germanosilicate SSZ-75 can also be used as a catalystfor converting oxygenates (such as methanol) to olefins, in thealkylation of aromatics, in reforming reactions, or for making smallamines. Germanosilicate SSZ-75 can be used to reduce oxides of nitrogenin gas streams (such as automotive exhaust). Germanosilicate SSZ-75 canalso be used as a cold start hydrocarbon trap in combustion enginepollution control systems. Germanosilicate SSZ-75 is particularly usefulfor trapping C₃ fragments.

EXAMPLES

The following examples are given to illustrate the present invention. Itshould be understood, however, that the invention is not to be limitedto the specific conditions or details described in these examples.

Example 1

4.6 g of a hydroxide solution oftetramethylene-1,4-bis-(N-methylpyrrolidinium) dication SDA ([OH—]=0.69mmol/g) was added to a Teflon cup (for a Parr 23 mL autoclave). Next,0.015 g of SSZ-75 seed crystals, 0.110 g of ammonium fluoride, 1.5 g oftetraethylorthosilicate (TEOS) and 0.18 g of germanium ethoxide wereadded. The Teflon cup was covered with PARAFILM® and stirred overnightat room temperature to allow for hydrolysis of the TEOS. Then thePARAFILM® was removed to permit evaporation of ethanol and excess water.Following evaporation, an appropriate amount of water was added to theTeflon cup giving a final gel molar composition of 10 Si:Ge:4.4 OH:4.4NH₄F:77 H₂O. The mixture was stirred until homogeneous. At this point,the Teflon cup was closed and sealed in a stainless steel autoclave. Thereaction was heated at 170° C. while rotating at 43 rpm for 7 days. Uponcrystallization, the gel was recovered from the autoclave, filtered andrinsed with deionized water.

Powder XRD of the dried product crystals confirmed the sample to havethe stilbite structure (see FIG. 1).

SEM of the as-made material shows plate-like crystals (see FIG. 2).

Example 2

3.32 g of a hydroxide solution oftetramethylene-1,4-bis-(N-methylpyrrolidinium) dication SDA ([OH—]=1.04mmol/g) was added to a Teflon cup (for a Parr 23 mL autoclave). Next,0.015 g of SSZ-75 seed crystals, 0.110 g of ammonium fluoride, 1.5 g ofTEOS and 0.364 g of germanium ethoxide were added. The Teflon cup wascovered with PARAFILM® and stirred overnight at room temperature toallow for hydrolysis of the TEOS. Then the PARAFILM® was removed topermit evaporation of ethanol and excess water. Following evaporation,an appropriate amount of water was added to the Teflon cup giving afinal gel molar composition of 5 Si:Ge:2.4 OH:2.4 NH₄F:35 H₂O. Themixture was stirred until homogeneous. At this point, the Teflon cup wasclosed and sealed in a stainless steel autoclave. The reaction washeated at 170° C. while rotating at 43 rpm for 7 days. Uponcrystallization, the gel was recovered from the autoclave, filtered andrinsed with deionized water.

The Si to Ge mole ratio of the product was determined to be 6.7 by ICPanalysis.

Powder XRD of the dried product crystals confirmed the sample to havethe stilbite structure (see FIG. 3).

SEM of the as-made material shows plate-like crystals (see FIG. 4).

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that can vary depending upon thedesired properties sought to be obtained by the present invention. It isnoted that, as used in this specification and the appended claims, thesingular forms “a,” “an,” and “the,” include plural references unlessexpressly and unequivocally limited to one referent. As used herein, theterm “include” and its grammatical variants are intended to benon-limiting, such that recitation of items in a list is not to theexclusion of other like items that can be substituted or added to thelisted items.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope is defined bythe claims, and can include other examples that occur to those skilledin the art. Such other examples are intended to be within the scope ofthe claims if they have structural elements that do not differ from theliteral language of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims. To an extent not inconsistent herewith, all citationsreferred to herein are hereby incorporated by reference.

The invention claimed is:
 1. A crystalline molecular sieve having STItopology and having a silicon to germanium mole ratio of less than 15.2. The molecular sieve of claim 1 having, after calcination, an X-raydiffraction pattern substantially as follows: 2-Theta d-Spacing RelativeIntegrated (degrees) (Angstroms) Intensity (%) 10.00 ± 0.20 8.83 VS13.14 ± 0.20 6.73 W 19.38 ± 0.20 4.58 M 21.03 ± 0.20 4.22 M 22.35 ± 0.203.97 VS 24.19 ± 0.20 3.68 W 26.43 ± 0.20 3.36 M 28.37 ± 0.20 3.14 W30.16 ± 0.20 2.96 M.


3. A crystalline molecular sieve having a composition comprising,as-synthesized and in its anhydrous state, in terms of mole ratios, thefollowing: Si/Ge <15 M_(2/n)/Si   0 to 0.03 Q/Si 0.02 to 0.08 F/Si 0.01to 0.04

wherein M is an alkali metal cation, an alkaline earth metal cation or amixture thereof; n is the valence of M; Q is atetramethylene-1,4-bis-(N-methylpyrrolidinium) dication; and F isfluoride.
 4. The molecular sieve of claim 3, wherein the Si to Ge moleratio is from 3 to 12.